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Townes Lectures on Black Hole

By Dana Levine

EXECUTIVE EDITOR

Nobel laureate Charles H. Townes gave a lecture last night discussing the research that proved the existence of a black hole at the center of the Milky Way galaxy.

The talk, the second of the Ford/ MIT Nobel Laureates series, was entitled “The Black Hole at the Center of Our Galaxy.”

Townes received the Nobel Prize in 1964 for his work in quantum electronics, which led to the construction of oscillators and amplifiers based on the maser-laser principle. He holds the original patent on laser technology along with his brother-in-law, A. L. Schavlow.

Townes served at MIT as Provost and Professor of Physics from 1961-1966, and was named Institute Professor in 1966. In 1967, he left MIT to become a University Professor at the University of California.

The center of the galaxy

Until recently, astronomers were unable to see into the center of the galaxy, and many people did not realize that the earth lay within a galaxy. “It was only the middle of the last century that we realized, ‘Hey, we’re in a galaxy,’” Townes said.

Dust particles block all visible forms of radiation, preventing astronomers from viewing our galaxy. In 1932, Karl G. Jansky built a radio telescope and used it to monitor microwaves coming from outer space.

It was soon discovered that these radio waves originated in the center of the galaxy. Work in the late 1960s showed that infrared rays also are emitted from a similar location in space.

More recently, the construction of a 27-antenna National Radio Astronomy Observatory in New Mexico has allowed for even more precise measurements. “It’s almost as if they’re dancing together,” Townes said of the antenna array.

Radio waves, which allow for better angular resolution than optical waves, allowed astronomers to see a “bright center” of the galaxy, a spot which emits a large amount of radiation. This bright center has been named Saggitarius A, and emits 10,000 times as much light as our sun.

Evidence points to black hole

When an electron and a positron collide, gamma rays are emitted. Through the use of interferometry, researchers managed to find evidence of this type of collision in the center of the galaxy, which is characteristic of a black hole.

Within a black hole, the gravitational force is so strong that no matter can escape. “The center of our galaxy is the natural place. Things fall in, things accumulate there,” Townes said. “We’ll all fall in, eventually, in 100 million years or so.”

Soon Townes and his associates at the University of California, Berkeley began to study the evidence. They traveled to an observatory in Chile, which has a particularly calm atmosphere.

“We went down to Chile, partly because of the good atmosphere, but partly because the galactic center passes right over there,” Townes said.

By studying gas ions in the bright center, Townes determined that a ring of gas rotates in a nearly steady orbit. While the gravitational force of the mass within the orbit appeared to be nearly 3.5 million times that of the sun, the object itself was rather small.

“We thought we could argue very strongly that there was a black hole there because of the velocity of the gas,” Townes said. The discovery of this black hole was confirmed when stars were found that rotate around the black hole. The velocity of the stars was similar to that of the gas particles.

However, there are several unanswered puzzles which relate to the newly discovered black hole. For example, it only emits one-thousandth of the radiation that its size would suggest.

Townes believes that these unanswered questions could lead to breakthroughs in black hole research. “The lack of illumination from Saggitarius A is perhaps the most serious discrepancy, but also the most exciting,” Townes said.